Butadiene, an important basic fraction, is used as an intermediary for various petrochemical products, and demand and value thereof are gradually increasing in the petrochemical market.
Butadiene can be extracted from the C4 fraction through naphtha cracking or obtained by direct dehydrogenation or oxidative dehydrogenation of butene.
Thereamong, according to the method of preparing butadiene through oxidative dehydrogenation of butene, oxygen is used as a reactant, and two hydrogens are removed from butene to generate butadiene. In this case, water generated as a result of the reaction is stable. Thus, the method is thermodynamically very advantageous. In addition, since oxidative dehydrogenation is an exothermic reaction unlike direct dehydrogenation, butadiene may be obtained in high yield even at low reaction temperature as compared with direct dehydrogenation. Therefore, using the method of preparing butadiene through oxidative dehydrogenation of butene, it is possible to effectively meet increasing demand for butadiene.
In addition, according to the method of preparing butadiene through oxidative dehydrogenation of butene, in addition to raw materials, nitrogen, steam, or the like is added as a diluent gas for the purpose of reducing explosion risk due to oxygen and for removal of heat of reaction. When hydrocarbons are separated from reaction products including diluent gases, light gas species (COx, O2, and the like), hydrocarbons, and the like, a method of absorbing hydrocarbons from reaction products or a method of liquefying hydrocarbons by cooling reaction products may be used. Thereamong, the absorption method is mainly used. In the case of the liquefaction method, a very low-temperature refrigerant is required for liquefaction due to diluent gases, light gas species, and the like present in reaction products. This increases equipment costs, operating costs, and energy consumption, which may lower economic efficiency of processes. For this reason, the absorption method is preferred.
In this regard, FIG. 1 shows a schematic diagram for explaining a conventional device for preparing butadiene and a conventional method of preparing the same.
Referring to FIG. 1, the conventional device includes an oxidative dehydrogenation reaction part 110 responsible for generating reaction products including butadiene from reaction raw materials including butene, oxygen (O2), steam, and nitrogen as a diluent gas; a cooling separation part 120 responsible for separating water from the reaction products generated through oxidative dehydrogenation; an absorption separation part 130 responsible for separating butadiene or a C4 mixture containing butadiene, and hydrocarbons from the oxidative dehydrogenation reaction products, from which water is separated; and a purification part 140 responsible for purifying butadiene from the butadiene-containing stream separated in the absorption separation part 130.
The oxidative dehydrogenation reaction part 110 may be operated to react reaction raw materials including butene, oxygen (O2), steam, a diluent gas (N2), and unreacted butene recovered in the purification part in the presence of a ferrite catalyst or a bismuth molybdate catalyst under isothermal or adiabatic conditions.
The cooling separation part 120 may be operated by a quenching-type direct cooling system (quencher) or an indirect cooling system.
FIG. 1 shows an example of selectively absorbing and separating only butadiene in the absorption separation part 130. In the absorption separation part 130, only butadiene may be selectively absorbed from reaction products from which water is separated, or all hydrocarbons including a C4 mixture may be absorbed using a solvent. Specific examples of solvents capable of selectively absorbing butadiene may include acetonitrile (ACN), N-methylpyrrolidone (NMP), dimethyl formamide (DMF), and the like, and specific examples of solvents capable of absorbing all hydrocarbons including a C4 mixture may include toluene, xylene, and the like. In the absorption separation part 130, COx, O2, and N2 used as a diluent gas are all incinerated, or in some cases, a portion thereof is recovered in the reaction part and reused, and the remainder is incinerated.
For example, the purification part 140 is conventional butadiene purification equipment. In the purification part 140, an acetonitrile (ACN) process, a N-methylpyrrolidone (NMP) process, or a dimethyl formamide (DMF) process may be performed. When necessary, parts of these processes may be performed in modified form to purify butadiene.
However, in general, an excess of a solvent is used in an absorption separation process. Thus, a large amount of energy is consumed in the process of recovering an absorption solvent and the process of recovering and purifying butadiene in the purification part 140. Alternatively, when the absorption separation process is replaced by a condensation process, a very low-temperature refrigerant is required. In this case, energy consumption, raw material costs, and production costs are increased, thereby lowering economic efficiency of processes. Therefore, there is an urgent need to develop related technologies to solve these problems.